The present invention relates to ignition systems for internal combustion engines, and more particularly the invention relates to an ignition timing control system having an acceleration ignition advance function which ensures the best performance of the engine during the periods of acceleration.
The ignition timing of an internal combustion engine must be determined in accordance with the operating conditions of the engine to ensure the optimum operation of the engine. The ignition timing control systems known in the art are of two general types, mechanical and electrical systems. With either of these two types, it has been the usual practice to utilize the engine speed and intake vacuum as two basic factors for determining the ignition timing and control the ignition timing in response to these two conditions. Thus, with either of the types, two preliminarily programmed ignition timing characteristics, i.e., characteristic .alpha.N using only the engine speed N as a variable and another characteristic .alpha.P using only the intake vacuum P as a variable are employed so that in the actual operation of the engine the ignition timing is determined in accordance with the sum .alpha.N+.alpha.P of the values respectively corresponding to the engine speed N and intake vacuum P, and no provisions are made to provide the required acceleration compensation during the periods of acceleration operation where the engine throttle valve linked to the accelerator pedal is opened rapidly.
However, during the periods of acceleration, particularly during acceleration operation of the engine from the cold, when the accelerator pedal is moved rapidly, even if the air-fuel ratio of mixture is adjusted by the carburetor or the like, the resulting atomization of the fuel generally tends to become unsatisfactory, thus causing the fuel to stick to the walls of the intake pipe or increasing the diameter of the fuel droplets and thereby causing the production of nonuniform mixture. With the cold engine, the temperature of the intake pipe walls is particularly low with the resulting decrease in the amount of carburetion and this has a great detrimental effect. If such a nonuniform mixture is drawn into the combustion chamber, the mixture will not be burned completely and hence a sufficient torque will not be produced, thus producing only a gradually increasing torque.